Isomerization of light naphtha



Nov. 2l, 1950 B. H. GWYNN ET A1. i 2,530,875

ISOMERIZATION 0F LIGHT NAPHTHA Filed Aug. 29, 1947 atented Nov. 2l, 1950 UNITED iSTAT'ES PATENT OFFICE I'soMERizATiovslonr NAPHTHA Bernard H. Gwynn, 'llarentnm` and Charles Montgomery, Oakmont, Pa.,l1a`ssignors to Gulf Research&. Development Company, Pittsburgh, i Pa., a corporationlofelaware Applicationy August 29, 1947,- Serial No 771,370

pressure operation and 'they` introduce `into vthe processes undesirable Vmaterialswhich must be subsequently removed. VIt has` also been proposed `heretofore to* isorn'erize` 'naphthas .in the presence of a` large' proportionfoffa low' boiling isoparain, such" asis'obutane or isopentane. large' proportion of isopentane added -to anaphtha, 'liowevc-n,V hasl a tendency "to subdue the isomerization of normal pentane` irrfavor `ofiA the isomerization ofnormal hexane;

It is' an object achieved .by this invention toi provide an improved' light naphthavisomerlization processduwhich increased.' yieldsvofwisopentane; neoh'exane andfisohexanes; aref obtained.

Another`v object achievedlby' this-inventiorr is toprovide a `process for improvingI the'lisoparaflin content of a light naphtha wherein the amount of' added isopentanev cracking inhibitor iswmater'ally decreased.

Another object' achieved by this invention-ds to provide an improved processfcr the i'scmeriza-` tion of a light naphthaiat al relatively low :ternperature in which a product consistingiessentially of pentanesfand hexanesis obtained `without resorting to fractionationifor the separation of a diluent*cracking'inhibitor.` o

A further object achievediby this invention is to provide an improvedprocess `for theisomerization of a light naphtha of' the pentanehexane boiling 'range' in 'which #the pentaneV .fraction of the productconsistswof van equilibrium mixture of normal `pentane .andwisopentane A further object 'achieved by 'this invention is to provide an improved process for theisomV erization of a light -naphthaotlthe pentanehexane boiling rangewherein the isopentane produced in the isomerization of the normal-pentane serves a5 a" cracking inhibitor' during thev isomerization of the normal hexane.

A still further objectachieved by thisl inven tion `is Vt Vprovide an improved light naphtha isomerization process iniwhich the yformation-of aluminum halide-hydrocarbon `complexes is minimized and improved use lis made of the catalytic activity of the aluminum halide.

Qther objects achieved by `this invention 'will `become apparent in the following detailed 4description thereof. A

Wehave discovered thatV increased yields of isopentane, neohexane, `and isohexanes can be obtained during the isomerization of a light naphtha of the pentane-hexane boiling range in. the presenceof an aluminum. halide catalyst and a hydrogen halide. promoter if the light naphtha is fractionated into-aCs` fraction and a Ce fraction, each fraction then being separately isom-I erizedin the presence ofa predetermined amount ofisopentane o Inpracticing our invention,we fractionate a light naphtha intoa Ca hydrocarbon fraction,

`a Cs hydrocarbon fractiomand .a C7 and heavier hydrocarbon fraction. The latter fraction may be blended with. the uiinal product or may be discarded. The C hydrocarbon .fraction isv treated according to our copending application, S.. N. 717,010, whereby a mixture .-of liquid normal;

pentane and isopentana. `said mixtureA containing about 33 to 5()` per cent by Weight o f isopentane, is contacted with an aluminum. halide and hydrogen halide in a reaction` zone `at a tem perature below about '70 C.; a reaction `mixture containing substantially more isopentane than was present in the charge and not more than about percent by weight of isopentane is withdrawn from Isaid reaction zone. According to lthe present invention, an equilibrium mixture consisting of about 85 to about 90 iper cent by weight of isopentane and. about 1 5ito about l0 per cent by Weight of normal pentane is obtained from Athe reaction mixture produced in kthe pentane. isomerization step. .The equilibrium vmixture .is mixed with the Ce hydrocarbonfraction inv an amount sufficient to produce a lmixture containing at least about 45 per cent by Weight of .isopentane. The pentane-hexane mixture is lcontacted `with. an active isomerization catalyst, Y.such asan aluminum halide..and auhydrogen halide `promoter ina hexane :reaction zone at a temperature below about C. Whereby normal hexane isA converted predominantly to neohexaneandfisohexanes. Arr improved light naphtha-:is.-recoveredthe pentane content of said.- improved light naphtha consistingessentially of anequilibrium mixture of normal 4peritaneand isopentane. If desired, the product recovered may contain pentanes and hexanes in the same relative proportion as was present inthe light naphtha prior `to its `initial .fractionation into Aa Cahydrocarbon fraction, a Ce hydrocarbon fraction and a Cv and-heavier hydrocarbon fraction. fil-151e C5 fractionxofotheproduct. however, wouldconsist of anaequilibrium'mixtureor about .tol about/*9G per cent byHweight of isopentane.

:.As. pointed outiinlour 4copending application, SiN. .\717,010,.increased yiel'dssof isopentanefcarr be obtainedduring theV isomerization of normal lesaurire 3 pentane in the presence of an aluminum halide catalyst and a hydrogen halide promoter if a predetermined amount oi' isopentane is introduced with the normal pentane to be isomerized. For example, We determined that isopentane yields above about 50 per cent could be obtained ir" the normal pentane to be isomerized is mixed with isopentane in an amount corresponding to about 33to about 50 per cent by Weight or' the mixture.V

li' less than about 153 per cent or more than about 50 to 52 per cent by Weight of isopentane is present initially in the normal pentane feed, the yield of isopentane is less than the yield without the presence of any initial isopentane. Particularly good Ayields 'of isopentane are produced without substantial cracking ii' the proportion of isopentane in the pentane feed is maintained at between about 35 per cent and about 45 per cent by weight oi the total pentane feed and best yields are obtained with an initial isopentane concentration or' about 4U to 4l per cent. We determined that I'or the greatest eiiiclency the reaction mixture Withdrawn i'rom tile pentane reaction Zone should contain not more than about o per cent by weight of isopentane. The process can be operated to produce a product containing more than about 60 per cent or' isopentane, but when greater than about 60 per cent oI isopentane is obtained in the product stream, there also are obtained considerable amounts oi cracking and decomposition products with accompanying side reactions and deterioration of the catalyst taking place. Accordingly, when the product stream contains more than about 60 per cent by Weight oi isopentane, the advantage gained by the initial isopentane concentration is oiiset by the formation oi side reaction products. The pentane isomerization step is, tnerelore, most advantageously carried out with an initial isopentane concentration of about 40 to 4l per cent and a iinal isopentane concentration not greater than about cc per cent. Conversion or normal paritarie to isopentane taking place during a single pass through the reactor' is relatively small; however, the cii'cuiation rate is suiilciently i'ast to give a commercially attractive process.

`We have round that increased yields of neohexane and isonexanes can be obtained during the isomerization of normal hexane in the presence of an aluminum halide catalyst and a hydrogen halide promoter if a predetermined amount oi' isopentane is introduced with the normal hexane to-,be isomerized. For example, we have found that neohexane and isohexanes are produced with a minimum amount of cracking occurring if the normal hexane to be iscmerized is mixed with isopentane in an amount corresponding to at least about 45 per cent by Weight o1 the mixture. If less than about 45 per cent by weight of isopentane is present initially in the normal hexane feed, the amount of cracking occurring is substantially increased and the yield of isomerized hexanes is substantially decreased. Particularly good yields or" neohexane and isohexanes are produced Without substantial cracking if the proportion of isopentane in the hexane feed is maintained at between about 45 percent and 55 per cent by Weight of the total hydrocarbons present in the hexane reactor. The isopentane concentration may be as high as 75 per cent or even higher; however, from an economic standpoint Yit is generally desirable to use not more than about 55fper cent by weight. The isopentane used as the cracking inhibitor in the hexane reactor may halide promoter.

be substantially pure isopentane but more advantageously it is an equilibrium mixture of normal pentane and isopentane; that is, a mixture consisting oi' about 85 to about 90 per cent isopentane and about 15 to about 10 per cent normal pentane. We have found that when substantially pure isopentane is used, there is a tendency ior a portion of the isopentane to be isomerized to normal pentane until an equilibrium mixture is obtained. When using an equilibrium mixture of normal pentane-isopentane, the amount of mixture used as inhibitor is greater than the amount of pure isopentane used because in the mixture the normal pentane acts only as a diluent. Thereore,`if an` equilibrium mixture consisting of 10 parts normal pentane and 90U parts isopentane is used as the cracking inhibitor, the minimum amount or mixture that can be used is -50 per cent by weight of the nal pentanehexane mixture. In such a case, amixture will result consisting of 5 per cent normal pentane, 45 per cent isopentane, and 50 per cent hexanes'.

The amount of isopentane reported hereinabove to be required to inhibit cracking reactions during the separate isomerization of normal pentane and normal hexane is based upon the use of an aluminum halide catalyst and a hydrogen Theparticular ranges of isopentane concentration cited, however, may vary depending upon the particular catalyst employed and depending upon the operating conditions such as temperature, pressure and space velocity.V

lt should be understood, therefore, that the optimum isopentane concentration at a given ternperature, pressure and space velocity will varyv with the particular catalyst but can readily be` determined in a few trial runs.

The embodiments and examples recited herein have, for the sake of simplicity, been restricted to aluminum chloride as the catalyst and hydrogen chloride as the promoter. It should be understood. however, that we do not Wish to limit this invention either with respect to a particular catalyst or with respect to a particular promoter, l

The yields referred to herein are a measure of the efficiency of the conversion of normal hydroriarbons to isomerized hydrocarbons and are calculated by dividing the moles of isomerized hydrocarbons formed by the moles of normal hydrocarbon converted all multiplied by 100.

The naphthaJ employed as charge steek, according to the process of our invention, may be a light virgin naphtha or any naphtha fraction talli-c halide-hydrocarbon complexes, thus causing substantial catalyst deterioration,

The catalyst used in either the pentane reactor or the hexane reactor can be any of the active isomerization catalysts such as metallic halides, boron trifluoride, hydroiiuoric acid, and the like. While any of the anhydrous metallic halides will -function as isomerization catalysts, for practical purposes aluminum halides, such as aluminumv chloride and aluminum bromide are preferred. These halides can be used alone or in combination with a carrier or support material, such as Zeolite, permutite, and the like. If desired, the aluminum halide can be suspended or dissolved Olenic and aromatic hy-` ti9l15`LCr CFL. .v use on axnoit corresponding.. 2 and about 4 per cent by weight. based onthe Weight. Ot-tho.. hydrocarbons'tptesontinlthe.,reacf tion. Wehaifeioondthatif.less thanabout 211er. oontby. Woiehtof ahrdrogenhalideis used. thgur raoidlyaand th ine `..introases. rather... rapdlya..

,The Operating.. .7..C0ndti0ns,. such s as tempera.-

turned1 pressure, and space.. velocity; employed in the two, reactors .are substantially thesame Naturally, these. .conditions ,willi/ary depending upon the particular catalyst choseni The...1-eactions cambeeffectedffor instancefpver a Wide range of the.;.aotirity ,.Of.; ccordane fivithw hrdrocerbonioonvereiondrops. .if...m0.r.e .thanabout percent o.. a hydrogen,halide vis. used, l the. .amount of.. cr,ack.

-: o between. about not more than about 50 to 55 per cent.

` the present, ,1

space ...velocitiesf In generaL-space.velocities of fromaboutl to.4.or.5 volumes. ofliquid feed. per` volumeuof/ catalyst per `houruare` employed.v The particular.space.fyelocityuemployed is adjusted so as .to obtain. satisfactory. .conversions .at the Atem.-

perature .chosein In. carrying. outnthe process. of our. inventionl the,v pentane.. .,isornei'izationt reaction andthe` hexane isomerizationreaction. are carried out at drooarbousim ...duit ll intowfra adinto, airaetl.

a temperature .belowu about. .709 Cp and.; about 75"9-.C., re'spectivelyt. Theer'eactionsaretpreferably carried outat. a, ytemperature:.within=the .range ofl about .40. Cato about .7609 Cw` In general, ternperatureshigher than. about .70?A in Ythe pentane reactor. and 'lC'fin theI .hexane reactor are l undesirable .because `at. thesetemperatures the isomerization... reaction isaccompanied t by.y increased `cracking andV otherdecompositionreactions. The minimum-temperature at which our invention may be practicedin either `reactor dependsupOnwhether` the `process is being carried 'j out in the liquid phase or'the vaporphasel Our processcan-be carried outin theliquid phase at a temperature less `thanfiOj C., but Vfrom a commerciall standpoint, 4the temperature is adva-n` .tageously-above about 4090s If a highly -active ycatalyst and promoter are? used, `wel -mayernploy temperatures even. asloW as- 259C.` Vapor-phase isomerization` naturally-must -be Vcarried out ;abovethe :boiling point 'lof the normalpentane 1 and normal hexane,i respectively. Liquid phase ;somerization is carried out under-a pressurelsuffcient to maintain -thereac-tants in :liquid phase. .A `pressureoi.200;.to250 s. ;i.-shou1d1 be.ade-

quatel to maintain thewreactants in .a liquid phase .c

:ata temperature of .75"v C, or less.

Our invention ,maybaapplied .to isomerization inliquid.phase.vapor.phase,vand mixed liquor- 'vapor phase.. Howeverfourinvention is most :advantageously applied to1-liquid .phase .isomeri-l zation` because of certain economic advantages.. obtained byliquid phase. isomerization There.

fore, while our inventionislhereinafter described inconnection l.fwitln itsaprefenred embodiment,

.our .proeessderelopsiroot thefaetthat, a ,create .il

yield .of high octa .onidetaifi .0f,..the .following detailed .doser f tion4v illustrating.-` the..preferredmethods,of` prac ze on? .protest vaporiphlaol V Oilr irirehtoo.istpentiouletlr advantageous i that ..110.. dilten .1s Lirittodueed.irito .the ...De reactosystom-t Aseordioslrltho protest-oto inventionis `@201.10unical, in that .frac onatiQn f adiluent cracking. inhibitorfisavoide Our i ..,rat.ine.blondinsfuel is 0b@ tained.than.hasfhorotoforelbee obtained F9 examplathepentous fraction., mayontain upwardsof 180,.forxa .pla 35.: per.l `.cent enamore., ofisop'entana whereas usu isV present `in theporttane Other advantages-...of our...inyentionawllfqbea, come .apparentto thoseskilled.inthe eport...`

tting the process,Y of ourinver,1tion It` islto .b I, understood.thatnumerous modioatiens may .be-.1 made inthe schematic. `flow .diagram shownain the' accompanying drawing Y,wi.mout. ...donating from.,

Nowreferrins to.. the fleure lglltilaphths Sistine; predomin' tly .of...Ct` andepar..-

through oooluitfld. 1f. anrhoptanes. and heerlen...

,hydrocarbons are presentQtheymay. begwithdravvriv V throughv valvdfcoiiduit. I5. d

The pantano fractionwithttewn.tnrellehooua duit i3 Yfromtho top of iractionator Izis mixedi with normal pentangeycle; coming.fromA the.

valve 5 4,.and conduit 55. Thecombined pentane. feed then passes into conduiti where it is mixed,r`` with hydrogen .chloride froinconduiti 9 andprpd uct recycle Streamirom, Conduit` ,2li` containing...

pentane. The hydrogen 'chlordlewin conduit i9, consists of fresh hydroge =`chloride. introdu through` conduit., 2 lfanlvolrgs. .22v .andlandre cycled hydrogen chlorideintroduced,.throughgonfi` Th pentanerilrdmgen GhlQride Solution which.: is` formed nat the intersection,OLzcOnduits il 3, Ai 8 and 270 enters pumpdthroughcond t2?.V Tl'ie-..V

`,pumped into conduit; 28 froinwhch a.majnr.4

proportion is circulatedlbypump I26 through con-` duit 29 containing yalve .to `conduit 21. minor proportionofr the-pentane-hydrogen .chiot ride,y solutiony from` conduit 28 is iwitlrirayyn1 portionof. a pantano.. toaster-.33 whiottis edve taeeously maintained@ a-temperattlraef i0?- soso.

The .circulationoi a :maJ'QI `proporton offltheyfg.

y tpentanehydrogen chloride solution .through conduit 29 insures thoroughlmixingof thel normal... pentane introduced throughcondutJS with the hydrogen chlorideland .the .recyclevproduct stream introduced .throughsoaduitswif andrew, :respete mixture iconsisting of aboutlO percent isopentaneand about 60 per cent normal pentane. The reactor is then heated to about 50 C. and a normal pentane-isopentane-hydrogen chloride solution containing at least 33 per cent and not more 4than `50 per cent of isopentane vand 2 to 4 per cent of hydrogen chloride is then charged tothe reactor.

Only one pentane reactor is shown in the iigure; however, continuous operation may require several reactors so that when the catalyst in one reactor is reduced below an economic level, the flow can be diverted to another reactor while the depleted reactor is being recharged with fresh catalyst. `Pentane reactor 33 may contain solid aluminum chloride or aluminum chloride deposited on a suitable support or it may contain one of the various liquid catalysts wherein aluminum chloride is dissolved, suspended, or reacted with some organic or inorganic material. VIf solid aluminum chloride'is used as catalyts in hexane reactor 61, the sludge which forms therein can, if desired, be used as catalyts in pentane reactor 33. VPentane reactor 33 may be provided atits top with a plate 34 which can be removed when it'isnecessary to` charge the reactor with fresh solid catalyst. The reactor may also be provided at its bottom with a valved conduit 35 through which'catalyst sludge, if formed, may be withdrawn'or through which liquid catalysts may be introduced if desired:

"The pentanes, upon entering the lower portio'n' of pentan'e reactor 33 through a suitable distributing means (not shown), pass upwardly in contact with the catalyst during which passage ja portion of the normal pentane is isomerized to isopentane so that the resulting product stream contains not more than about 60 per cent isopentane. The'concentration of isopentane in the incoming stream is maintained'between about 33 per cent and about 50 per cent. The upper portion of pentane reactor33 is provided with a settling zone 35 to minimize catalystV carryover into theproductl and recycle lines. From the top oiV settling zone 3G, a product stream containing not more than about -60 per cent of isopentane is withdrawn through conduit 31. One portion of the product stream is recycled through valve 39 and conduit 2t to conduit I8 wherein'it is mixed with a predetermined quantity of normal pentane so that the resulting mixture contains less than about 59 per cent but more than about 33 per cent of isopentane. The portion ofY the product stream not recycled through conduit 29 passes from conduit 31 through conduit 39 and valve 4Q into separator 4i where any dissolved or entrained catalyst is settled out. The amount of product stream removed through conduit 39 is controlled by valve 49 so that the isopentane concentration at the top ofV the reactor does not exceed about 50 per cent.-

Separator-4l is provided at its bottom with valved conduit 42 through which settled catalyst can be periodically withdrawn. If desired, the settled catalyst can be recycled to pentane reactor 33. From the top of separator 4I a product stream is removed through conduit 43 to hydrogen chloride stripper 44. drogen chloride stripper 44, hydrogen chloride and non-condensabie gases are removed through conduit 45 and recycled in part through conduit 24 to the beginning of the process. A portion of the hydrogen chloride recycle may be removed by valve 46 through conduit 41 to prevent light hydrocarbon gases that might be formed from building up in the system. From the bottom of hydrogen chloride stripper 44, a

liquid product is removed through conduit 48 to Y example, if the naphtha charge consists of equal parts or" normal pentane and normal hexane, the flow might be as follows: one hundred parts of a 56-50 mixture of normal pentane-normal hexane enters fractionator I2 through conduit II. 'Fifty parts of normal pentane are removed from i'ractionator I2 through conduit I3 wherein the 50 parts of normal pentane are mixed with 40 parts of normal pentane recycle coming from the bottom of fractionator 4t through conduit 53, valve 54 and conduit 55. The 90 parts of normal pentane are then mixed with at least 180 parts of a 50-50 mixture of normal pentaneisopentane recycle coming from the top of pentane reactor 33 through conduit 31, valve 39 and conduit 29. The hydrocarbons thus entering the bottom of pentane reactor 33 consist of 90 parts of isopentane and 180 parts of normal pentane. The isop-entaneV concentration in the mixture accordingly is about 33 per cent. From the top of pentane reactor 33, 270 parts of a 50-50 mixture oi normal-pentane-isopentane kare withdrawn through conduit 31; 180 parts are recycled as mentioned above and the remaining parts pass through separator 4I and hydrogen chloride stripper 44 to fractionator 49. From the top of fractionator 49, 45 parts of isopentane are removed through conduit. From the bottom of fractionator 49, 45 parts of normal pentane are withdrawn through conduit 53. Forty of the forty-five parts of the normal pentane are recycled through valve 563 and conduit 55 and the remaining 5 parts are passed through conduit 56 and valve 51 into conduit I4. An alternate procedure would be to remove these 5 parts of normal pentane together with the 45 parts of isopentane through conduit 5i). The 45 parts of isopentane and 5 parts of normal pentane thus removed from fractionator 49 are mixed with the 50 parts of normal hexane coming from fractionator I2 through conduit I4. The hydrocarbon charge thus entering hexane reactor 61 consists of a mixture of normal hexane and pentanes, said mixture containing 45- per cent of isopehtane. An isomerized product consisting of 50 parts pentanes and 50 partsv hexanes is withdrawn from the top of hexane re- Y actor 51 andY passes through separator 12 to Vhydrogen chloride stripper l5. In this particular case, fractionator 84 may be by-passed and the final products withdrawn from the bottom of hydrogen chloride stripper 15 through conduit 19, valve 80, conduit 8|, conduit 96, valve 95,

conduit 93, valve 9'2,.and valved conduit. 94 to From the top of hynormal bentaneandq per centln rmal hexane,

*bei QW meint-be at fellows? A en hundred Parts of aHO-fifmixture ofnormal pentane-normal hexane A' 'enters iracjtionator I 2 through conduit I lIl Forty partsof normal pentane areV removedr v,from fractionation I? through conduit I 3 wherein thfiO parts of normal pentane are mixed with 28 Qparts of 'normal n n tane recycle coming from .the bottomj of frac 1onator- 49 through conduit 53,

valve'54/ and cond'uitg55.` The 68 `partsiof normal `A pentaln are thenH mixed nwith atdleast 136 parts u Vo'f a'S-"SO mixture of `riormal pentane-isopentane Cleminafoel' that@ @f eentane reactor werden c dic 11 )hidroalfbdh this Yenfri1-ie ,i Q boitom of ntane lreactor tfconsist ci 68g parts of isoman@ and A136 Parts-,O inormalreilaneepihe ntanevconcentration in themixtureaccord- "ahout '33 `iper leent.` ironfiA-ighery ton.; of harte@ a mixture '-isepetanere rwith drawn 3l? 136` Darts are rees/,defies iraetonatom ,The .hiidroarbon charge reactorh] consists of a ne and pentanesmsaid 'r tapent Qi- ,isopentanextu're" n An isomerized produc` of hexane reactor Bland casses through separator 'I2 andhydrogen chloride stripper 'I5 to '.fractionator` Fioni'the t'p of fractionator 84, 2O parts of isopentane are recycled through conduufm. From the buntem, l lfinali procilucty consisting oiffl partspehtanes and 60 parts lliexaihesA is withdraiifnthrough valve 9 9, rconduits I9 a1`1d 93, vali/e321 and .valvedcondut '34 t'o storage V The peritanelcontent ofltl'i'enal jiiroductcons'sgt "per cent,V normal p entane.

charge consists 'fvi per cent normalpentane arid @per cent normal'hexane, the bw'iright he' as follows; 'onelundredfparts 'of a fio-4o 'inixturepf alrll hexane enters fractionation lgthroughlconduit I I. Sixty parts of normalpenta'ne are removed from t elfrartionator I thro-112fhcondi I Y normal aiie'ar ane-normal r L valve IIA and conduit 55,` "Thelilhparts of normal Upentanerarethenmixed with at least 224 `parts of a-- 50-50 IInixturepf Vnormal pentane-isopentanerecyclecoming--froms'the top of, pentaneu reactor 33 through; conduit-31; valve 38 -andicon- 16.1111211). lThelv hydrocarbonsthus entering-:the

bottom of pentane reactor 33 conSstiogfillZ parts of isopentaneand '224 partsqof Ynormal pentane 1corgiiri'gly,isaloout 33 PQI' Cent.- Frornthe top; of

jperntane reactor- 33,i 336gparts ofY `a- 5(1-50 mixture loft normalj pentane-isopentane are fwithdrawn through conduipl; `224;parts-are recycled as mentpned; abe-ver and thefremainine -112. parts pass through separator Iggand hydrogen chlor d :Stripper 4 4 to. fractionator 49w1Fromthe top of fracticnato rV 49,15parts of isciaentane are removedlthrough conduit 56: From' the-bottom arey withdrawnnthrough conduiti53. Fifty-two of the 56 parts ,of the normal pentane are recycled thijough-valve 54 and conduit 55 andthe jremaining 4 parts are-passed through conduit 56 Withdrawn from the top of isopentane,

v4charge. by means chloride in` conduit lchloride introduced through conduit 2I and valves duced through conduit 64 and valve 65.

and va1ve- 5l into conduit I4. -An alternative pro- Acedure Wouldrbe to remove these 4 parts of normal pentane together with -36 parts of isopentane as aside stream .ifrorn fractionator` 43 through Lvalve 58hand conduit\59; lrom'conduit 5l), 20 ,parts ofisopentaneare removed-through valve E0 and conduit 6I wherein; itsisl mixed with the .bottoms'f-rom hydrogen chloride stripperl thus forming the finaliA productf The remaining l36 y parts of isopentanefromconduit 59 pass through Valve `5I and` conduit 5,2 to conduit 66 wherein .A they are mixedi with-40 parts of normal hexane comingfrom fractionator` IZithrough conduit I4 and-4 parts ofnorrnal pentane coming fromithe bottom oi'ifractionator 19t-through conduit 56.

VThe hydrocarbon A)charge thusr entering; hexane reactor 61` consists-of arnixturefof normal hexane and pentanes, said mixtureContainingz45per cent An isomerfized product is withdrawn `frorrrthe:top of hexane yreactor 6I and passes through separator I2 to-hydrogen ch1oride 1stripper 15.: I n this case, fractionator '84 may beby-passed and thej isomerizedproduct withdrawn-from the bottom ofrhydrogen chloride `stripper I5 through conduit- 19, Valve 86, conduit 18|, conduit, valvez,` conduitl 93 and valve 92` to conduitEI -wherein it is mixed with the 20 partsoisopentane withdrawn from conduit 5).A The final blended product consisting of 60. partspentanes and 401 parts hexanes is WithdraWn through i valved conduitr 94 to storage. The pentane; contentof the nal blended `product consists of 933tper cent isopentane and 6.7 per cent normal pentane. i i

The hexane fractionwithdrawn from' fractionatorjli throughwconduit i4 is preferablymixed with an equilibrium mixture fof normal pentane 'and lisopentane obtained in accordance withlone ofthe abovemorir'ications. Hydrogen chloride promoter is introduced into the Dentaire-hexane f conduit 62. The hydrogen 62 consists ofV fresh hydrogen 2 2 and 63 and recycle'hydrogen chloride intro- The pentanehexane-hydrogen chloride chargepasses through-conduit@ intofthe lower portion of` hexane reactor A6l which is .advantageously maintainedat a temperature-cf 40 to 75 C. a

1U CQHtnU-OUS OperationM hexaneoreactorl 9011i eine an aluminum hauuecataiyst is ad- Yfllgwusly lled at the start of a run with a mixture consisting of about 50 per cent normal hexane and about 50 per cent of an equilibrium mixture of normal pentane and isopentane. The reactor is then heated to about 65 C. and a pentane-hexane-hydrogen chloride solution containing at least 45 per cent of isopentane and 2 to 4 per cent of hydrogen chloride is then charged to the reactor.

Only one hexane reactor is shown in the gure; however, continuous operation may require several reactors so that when the catalyst in one reactor is reduced below an economic level, the ow can be diverted to another reactor while the depleted reactor is being recharged with fresh catalyst. I-Iexane reactor 61 may contain solid aluminum chloride or aluminum chloride deposited on a suitable support or it may contain one of the various liquid catalysts wherein aluminum chloride is dissolved, suspended, or reacted with some organic or inorganic material. If solid aluminum chloride is used as the catalyst in pentane reactor 33, any slurry which forms therein can, if desired, be used as catalyst in hexane reactor 61. Hexane reactor 6l may be provided at its top with a plate 68 which can be removed when it is necessary to charge the reactor with fresh solid catalyst. The reactor may also be provided at its bottom with a valved conduit 69 through which any sludge, if formed, may be withdrawn or through which liquid catalysts may be introduced if desired.

The pentane-hexane-hydrogen chloride charge upon entering the lower portion of hexane reactor 61 through a suitable distributing means (not shown), passes upwardly in contact with the catalyst during which passage the hexane is isomerized. The upper portion of hexane reactor 67 is provided with a settlingr zone 'iii to minimize catalyst carry-over. From the top of settling zone l0, a product stream is withdrawn through conduit 'H to separator 'l2 where any dissolved or entrained catalyst is settled out.

Separator 12 is provided at its bottom with a valved conduit 13 through which settled catalyst can be periodically withdrawn. If desired, the setled catalyst can be recycled to hexane reactor 6l. From the top of separator 12, a product stream is removed through conduit 74 to hydrogen chloride stripper 15. From the top of hydrogen chloride stripper 75, hydrogen chloride and non-condensable gases are removed through conduit 'I6 and recycled in part through conduit 64. A portion of the hydrogen chloride recycle may be removed by valve 71 through conduit 'i8 to prevent light hydrocarbon gases from building up in the system. From the bottom of hydrogen chloride stripper 75, a liquid product is removed through conduit 19, valve 80, conduit 8l, valve 82, and conduit 83 to a fractionator 84. If desired, all or a portion of the hydrogen chloride stripper bottoms may be recycled to hexane reactor 61, through valve 85 and conduit 86. As shown hereinabove, if the original naphtha charge contains pentanes in an amount at least equal to the amount of hexanes, iractionator 84 may be bypassed and product may pass directly from the bottom of hydrogen chloride stripper through conduit 79, valve 86, conduit 9i, conduit 96, valve S5, conduit 93, valve 92 and valved conduit 94 to storage.

Fractionator 84 is provided at its top with a conduit 8l through which isopentane may be recycled. The amount of isopentane removed as overhead from fractionator 84 depends upon the composition of the original naphtha charge. 1f

(iii

the original naphtha charge contains more hexanes than pentane's, it has been shown above that isopentane is recycled from the top of fractionator 84 in an amount sufficient to produce a pent-ane-hexane mixture containing at least per cent of isopentane. If the original naphtha charge contains either more pentanes than hexlanes or equal amounts of pentanes and hexanes,

fractionator 94 may be by-passed. The bottoms from fractionator 84 pass through valve 96, conduit Si, valve 92 and conduit 93 into conduit 6 I If the original naphtha charge contains more pentanes than hexanes, isopentane coming from the top of fractionator 49 through conduitsm and 6| are blended with hydrogen chloride stripper bottoms, the iinal blended product being withdrawn through valved conduit 94.

The following is given as illustrative of the present invention, but it is to be understood that the invention is not restricted thereto. The data appearing for the four runs listed in the table below afford a comparison of the results obtainable when separately isomerizing normal pentane and normal hexane by contact with an aluminum chloride catalyst and a hydrogen chloride promoter in the absence of and in the presence of isopentane. All of the runs were batch liquid phase experiments, but it is to be understood that our process is also applicable to continuous operation. In each of the runs, mls. of charge was placed in a stainless steel bomb of approximately mls. capacity. To the charge was added 7.4 grams of anhydrous aluminum chloride. The bomb was closed and then immersed in a Dry Ice-acetone bath. When the bomb and its contents reached the approximate temperature of the Dry Ice-bath, 0.6 gram, or about 2 per cent by weight of the hydrocarbons charged, of anhydrous hydrogen chloride was added to the reaction mixture. The bomb was then attached to agitating means and immersed in a constant temperature bath. The pentane isomerization reaction runs 1 and 2 were carried out at a temperature of 48.6 C. for a period of 45 minutes. The hexane isomerization reaction runs 3, 4, 5 and 6 were carried out at a temperature of 30 C. for a period of 24% hours. When operating continuously we use'a temperature of about 65 C. and a liquid space velocity of about 0.2 to 0.6. After remaining in the constant temperature bath for the required time, the bomb was removed and quickly chilled in a Dry Ice-acetone bath. The bomb was then opened, the contents decanted and fractionated.

Table Runl Run2 Run3 Run4 Run5 Run Charge, weight Per cent:

n-pentane 99.0 55.0 n-hexane 100. 0 89.3 77.0 51.5 isopentane 1.0 45.0 l0. 7 23.0 48. 5 Product, weight per cent:

isobutane 21.9 0. 5 26. 4 25.0 29.0 0 9 n-butane. l. 4 l. 0 0 isopentane-- 30. 5 54. 3 17. 7 18. 2 19. 5 46.8 n-pentane.- 28. 1 44.0 2. 3 2. 4 3. 0 0 neohexane.- 7. 6 8. 4 l0. 4 2. 5 isohcxanes. 19 5 1 2 13.9 13. 3 12. 9 14.1 n hexanei--. 7.0 9. 0 3.1 35. 7 heptancs+---- 23. 7r 22. 7 22. 1 0 Yield, per cent 1-- 41. 5 84. 5 223. l 227. O 231. 5 i 105.1

1 mols. isomerized hydrocarbon formed hexane, the yields of isomer-ized hydrocarbons were substantially increased. For example, in run 1, where only 1 per cent of isopentane was initially present during the isomerization of normal pentane, a yield of only 41.5 per cent resulted. In run 2, however, wherein the initial isopentane concentration was 45 per cent, a yield of 84.5 per cent was obtained. Likewise, in run 3, where no isopentane was initially present during the isomerization of normal hexane, a yield of only 23.1 per cent resulted. While isopentane was present in runs 4 and 5, it was not present in an amount sufcient to suppress cracking as can be noted by the large amount of butanes formed. Also, it can be observed that the yields in runs 4 and 5 were only slightly higher than the yield in run 3 where no isopentane was present. In run 6, however, where the initial isopentane concentration was 48.5 per cent, a yield of 105.1 per cent was obtained. The yield of greater than 100 per cent is attributed to slight unavoidable errors in analytical determination.

This invention has been discussed with particular reference to certain embodiments and specic examples, but it is not limited to such embodiments or examples except as defined in the appended claim.

We claim:

A process of increasing the isoparain content of a light naphtha or the pentane-hexane boiling range comprising separating said naphtha into a pentane fraction and a hexane fraction consisting predominantly of normal hexane; admixing `with said pentane fraction normal pentane recycle and a proportion of normal pentaneisopentane reaction mixture sufficient to produce a normal pentane-isopentane charge mixture consisting essentially of normal pentane and isopentane and containing about 35 to about 45 per cent by weight of isopentane; isomerizing said normal pentane-isopentane charge mixture in the presence of an aluminum halide catalyst and a hydrogen halide promoter in a pentane isomerization zone at a temperature below about 70 C., said isopentane in said normal pentaneisopentane charge mixture acting to inhibit cracking of said normal pentane and being the 14 only cracking inhibitor present in effective amounts in said pentane isomerization zone; withdrawing from said pentane isomerization zone a pentane reaction mixture containing substantially more isopentane than was present in said normal pentane-isopentane charge mixture and not more than about per cent by weight of isopentane; dividing said pentane reaction mixture into two portions; recycling to the pentane isomerization zone one of said portions admixed with normal pentane as aforesaid, fractionating the remaining portion into a cut consisting essentially of normal pentane and a cut comprising isopentane; recycling normal pentane from said fractionation to said. pentane isomerization zone; mixing with the aforesaid hexane fraction a mixture of isopentane and normal pentane recovered in said fractionation and containing about 85 to 90 per cent by weight isopentane in an amount suicient to produce a hexane charge mixture containing at least about 45 per cent by weight of isopentane; isomerizing said hexane charge mixture in the presence of an aluminum halide catalyst and a hydrogen halide promoter in a hexane isomerization zone at a temperature below about C., withdrawing from said hexane reaction zone an improved light naphtha, said improved light naphtha containing unconverted normal hexane, a substantial amount of isohexane, and a pentane content consisting essentially of an equilibrium mixture of normal pentane and isopentane. y

BERNARD H. GWYNN. CHARLES W. MONTGOMERY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,305,253 McMillan Dec.. 22, 1942 2,335,406 Goldsby et al Nov.. 30, 1943 2,339,849 Goldsby et al Jan.. 25, 1944 2,393,051 McMillan et al. Jan. 15, 1946 2,399,765 Shoemaker et al. May '7, 1946 

